The quality of sound and video experienced in home entertainment systems or other audiovisual systems today is mostly determined by the quality of the components in the final stage of the signal path: the speakers and the display devices. These devices often are the main sources of infidelity in the audio/video reproduction. One reason is because these devices are open-loop systems. In other words, they do not have feedback mechanisms to compensate for variations and limitations in the transducers employed and the interaction of the transducers with the environment. Another reason is that these final stage devices commonly adhere to less stringent design specifications due to the prohibitively lofty costs associated with building high fidelity components.
Using high fidelity speakers as an illustration, an ideal speaker driver contains a magnet/voice (motor) assembly that perfectly converts an analog electrical signal into a particular force. This force then generates specific mechanical motion that quickly and accurately moves and stops the speaker cone in order to reproduce the identically shaped sound wave. Needless to say, in order to achieve such complex conversion from electrical signals to such precise mechanical motions, not only is much calibration most likely required, but parts specifically constructed to create particular amount of mechanical movements in the speakers are also needed.
There have been attempts to improve the final sound and video output quality. Some efforts focused on building even better and more precise speakers or display devices. Other efforts focused on generating sum and difference signals and using such signals to produce enhanced stereo signals. Yet other efforts focused on designing accurate equalizers where a particular signal's amplitudes within specific frequency ranges are either attenuated or boosted. Still others efforts involve having a trained technician apply audio test signals (i.e. tone bursts, sweep tones, white and pink noise, etc.) and video test signals (i.e. crosshatch, color bars, arrays of dots, etc.) to an audio/video equipment, compare the resulting output with the expected output, and manually adjust the audio/video equipment according to the comparison.
With the proliferation of high speed processors, real time execution of many signal or image processing algorithms is now possible. Since readily available semiconductor memories and non-volatile storage devices are capable of storing massive amount of data for long periods of time, the algorithms can be employed even when a significant delay exists between applying a signal to the input of the system and the effect of that signal on the output of the system. As a result, an apparatus or a general purpose computer system can deploy some of these signal or image processing techniques to actively monitor and correct the input signals of an audio/video system. When these input signals are modified to compensate for the shortcomings in both the intermediate and final stages of audio/video reproduction, the resulting audio/video output from inexpensive systems is capable of rivaling the output from high fidelity, but costly, audio/video systems.